The comedy improv in "Broadway's Next Hit Musical" moved from excellent to inspired Friday night at the Troy Savings Bank Music Hall when Deb Rabbai and Rob Schiffmann took off their shoes and socks, pressed their bare feet together and sang a love duet. They held hands and pumped their feet in a reciprocating motion, their chairs unexpectedly edging apart until they were improvising lyrics about aching legs, ailing spines and needing to take up yoga.

The audience howled. One of the joys of improv theater is rooting for the performers as they struggle to incorporate audience suggestions, then cheering as they succeed and go beyond expectations into comedic brilliance. The feet-and-toes duet, part of a made-up-on-the-spot musical called "A Mutant Among Us," was the highlight of many such moments on the Troy Music Hall stage Friday night.

The premise of "BNHM" is that the troupe — emcee, four performers, pianist — stage an awards show, with each of the performers devising a Broadway show tune based on audience suggestions plucked from a bowl. The crowd votes on its favorite tune of the four, and the performers create a 30-minute version of the show that contains it.

Rabbai's slip required her to sing a song titled "I Have 12 Fingers and 18 Toes" from a show called "A Mutant Among Us." The competing numbers were "Sparrow Bignight" from "A Murder in the Aviary," performed by Schiffmann; "The Too Little Jelly in My Jelly Doughnut Blues" from "Bring It On Bakery," performed by Becca L. McLarty; and "This Is the Silly Song of Slathering Slugs with Slippery Substances" from "The Worst Folk Singer Ever," performed by Jeff Scherer. (Stoddy Blackall was the versatile and witty pianist.)

Scherer, who was tasked with handling the "Slathering Slugs" tongue-twister, muttered "Goddamnit" when he read his assignment, which he tried to salvage by going to the bowl again; emcee Robb Coles commented later, "You have some of the longest song titles we've ever had."

Musical improv like this is never completely spontaneous, of course — the ensemble has a repository of song styles and genres from which to draw and enough experience with lyrical structure and rhymes to get the audience's suggestions, however unexpected, into the songs.

With that said, "Mutants Among Us" became an almost-plausible Broadway musical reminiscent of a 1950s sci-fi film. Rabbai played an alien sent to Earth to find a new home for her otherwordly civilization. When neighbors begin to suspect her, they investigate and discover her too-abundant digits as well as the things they all have in common.